1. Field of the Invention
The present invention is in the field of magneto-optical recording media containing a recording layer composed of a plurality of individual layers each of which contains a rare earth metal and a transition metal which vary in relative proportion between the individual layers.
2. Description of the Prior Art
There are magneto-optical disks suggested in the prior art which can be recorded on and/or read out by a laser beam such as a semiconductor laser beam. Such magneto-optical disks are commonly made of an amorphous alloy of a rare earth metal and a transition metal. A "transition metal" is defined as a metal in which the available electron energy levels are occupied in such a way that the d-band contains less than its maximum number of 10 electrons per atom and includes metals such as iron, cobalt, nickel, and tungsten.
It is common to use a sputtering process to obtain such a magneto-optical disk for use as a magneto-optical recording medium. In the past, a single sputtering source has been used to accomplish this result. The sputtering source or target is constructed such that pellets or other thin pieces of rare earth metal are located on a transition metal target. These metals are then simultaneously deposited on a substrate or base through a sputtering process.
FIG. 1 of the drawings illustrates a magnetization graph which plots intensity of magnetization against the intensity of the magnetic field of the magneto-optical recording medium thus made. As shown in FIG. 1, the prior art magneto-optical recording medium has a poor squareness ratio in its hysteresis characteristic. Accordingly, when an external magnetic field is applied to the record medium, the recorded level of the medium is deteriorated and hence the S/N (signal-to-noise) ratio is lowered. In addition, the conventional sputtering method has a defect in that it is quite difficult to obtain the magneto-optical recording medium as a uniform sputtered layer which has uniform magnetic characteristics over the entire area of the record medium.